Not applicable.
The present invention relates to ferroxanes and a method of making wherein a ferroxane may be defined by the general formula [Fe(O)x(OH)y(O2CR)z]n wherein x, y and z may be any integer or fraction such that 2x+y+z=3 and n may be any integer. The ferroxanes may be doped with at least one other element other than iron. The present invention further relates to a ceramic made from the ferroxanes of the present invention and a method of making. The present invention still further relates to supported and unsupported membranes made from the ceramic of the present invention.
Membrane mediated processes currently factor in solving many outstanding problems in engineering and technology including, but not limited to, water treatment, catalysis and fuel cells. Recent improvements in membrane materials and technology have collaborated to make membrane filtration economically competitive with traditional separation technologies for certain applications.
Inorganic membranes, because of a unique profile of characteristics, hold promise for application to specialized problems in science and engineering. Areas ripe for application of inorganic membranes include reduction of costs by capture of reusable by-products in the oil and petrochemical industry; improving efficiency of energy production from fossil fuels by cleaning the coal gasification process; removal of impurities and moisture from natural gas thereby improving the gas mining process; reducing waste in the pulp and papermaking process; and waste and water treatment.
Inorganic, e.g. ceramic or metallic, membranes have particular advantages over their organic counterparts. They are stable at high temperatures with ceramic membranes capable of operating at temperatures in excess of 1000xc2x0 C. and tend to be resistant to degradation in the presence of reactive chemicals. Because of the wide variety of materials that may be used in the fabrication of inorganic membranes, resistance to corrosive liquids and gases, even at elevated temperatures, can be realized.
Typical methods of manufacture for inorganic and/or ceramic membranes include powder processing and the sol-gel method; see, for example, Advances in Ceramics, Vol. 9., Eds., J. A. Mangels and G. L. Messing, American Ceramic Society, Westville, Ohio, 1984 and B. E. Yoldas, J. Mat. Sci. 1975, vol. 10, p. 1856.
Powder processing features the use of environmentally toxic binders and solvents such as trichloroethylene in the synthesis of the powder. Moreover, synthesis of the powder is a bottom-top approach, whereby discrete colloidal aggregates and particles are likely built up from dissolved single molecules of precursor compounds., As a result, particle size tends to be difficult to control using the powder processing method, most likely due to difficulties in controlling the rate of polymerization for assembly to the aggregates. The resulting collection of aggregates usually possesses a broad distribution of particle sizes, that is, it is said to have a low polydispersity index (PDI). The resulting mixture may be pressed, extruded or slip cast to provide the so-called green body, a ceramic precursor in the form of a single mass requiring only subsequent high-temperature thermal treatment to provide the final ceramic product. Ceramics ultimately attained from such a mixture of colloidal particles possessing a low polydispersity index tend to have a similarly broad range of pore sizes. For example, it is typical using this method to obtain average pore sizes between about 5 xcexcm (5,000 nm) and about 15 xcexcm (15,000 nm) in average size; and porosity between about 30% and about 50% pore volume. Ceramic membranes often comprise separate layers, each layer having a characteristic pore size. Large-pore size layers impart mechanical strength and often serve as supports for smaller-pore size layers that serve as the filtration membrane. Small pore layers may be obtained by coating with particles of suitable dimension prepared by a sol-gel process comprising, steps of dispersion, gelation, drying and firing. Crucial to this process is the creation of a stable liquid dispersion, or sol, of the colloidal ceramic precursors. This may be achieved through the use of numerous solvents and additives including strong acids, plasticizers and binders. These toxic agents, combined with sec-butanol which is a common byproduct of the process, are all environmental liabilities of the sol-gel process. The sol-gel also suffers from the general liabilities encountered in any bottom-top approach as described above.
Thus, there remains a need within the art for inorganic ceramics and membranes that can be produced with minimal environmental impact. In particular, the problem of producing iron oxide-based ceramics and membranes without wasteful byproducts remains less than completely solved. Moreover, the problem of producing iron oxide based ceramics and membranes with good control over pore size while simultaneously offering mild processing conditions has heretofore not been adequately addressed within the art.